1. Field of the Invention
The present invention relates to a liquid crystal display panel and a fabricating method thereof. More particularly, the present invention relates to a liquid crystal display panel adapted to minimize movement of a spacer, and a fabricating method thereof.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) device controls the light transmittance of liquid crystal material by using an electric field to thereby display a picture. The LCD device includes an LCD panel where liquid crystal cells are arranged in a matrix. The LCD device also includes a drive circuit used to drive the LCD panel.
The LCD panel includes pixel electrodes and a reference electrode, i.e., a common electrode, for applying the electric field to each of the liquid crystal cells.
Each of the pixel electrodes is connected to a thin film transistor (TFT) which is used as a switching device. The pixel electrode and the common electrode drive a liquid crystal cell according to a data signal supplied through the TFT.
LCD devices may broadly be classified into devices having a twisted nematic (TN) mode and devices having an in-plane switch (IPS) mode, according to the direction of the electric field which drives liquid crystal. In a device having a TN mode, a vertical direction electric field is applied. In a device having an IPS mode, a horizontal direction electric field is applied.
FIG. 1A is a diagram representing a TN mode LCD panel of the related art, and FIG. 1B is a diagram representing an IPS mode LCD panel of the related art.
Referring to FIGS. 1A and 1B, the TN mode LCD panel of the related art and the IPS mode LCD panel of the related art include an upper plate UP and a lower plate DP bonded to face each other with a ball spacer 36 therebetween.
Referring to FIG. 1A, the TN mode LCD panel of the related art includes an upper plate UP that includes a black matrix 2, a color filter 30, a common electrode 28 and an upper alignment film 24a sequentially formed on an upper substrate 31, and a lower plate DP that includes a TFT, a pixel electrode 22 and a lower alignment film 24b formed on a lower substrate 1.
In the TN mode LCD panel, the common electrode 28 is formed on the upper substrate 31 to enable the formation of a vertical electric field with the pixel electrode 22 which is formed on the lower substrate 1.
Referring to FIG. 1B, the IPS mode LCD panel of the related art includes an upper plate UP that includes a black matrix 2, a color filter 30 and an upper alignment film 24a sequentially formed on an upper substrate 31, and a lower plate DP that includes a TFT, a pixel electrode 22, a common electrode 28 and a lower alignment film 24b formed on a lower substrate 1.
In the IPS mode LCD panel, the common electrode 28 is formed on the lower substrate 1 in a stripe shape to be alternated with the pixel electrode 22 in a display area divided by the data line (not shown) and the gate line (not shown), thereby enabling the formation of a horizontal electric field with the pixel electrode 22.
Referring to FIGS. 1A and 1B, the black matrix 2 of the TN mode LCD panel of the related art and the IPS mode LCD panel of the related art divides the surface of the upper substrate 31 into a plurality of cell areas where the color filters in color filter 30 are to be formed. The black matrix 2 also acts to prevent an optical interference between adjacent cells.
The color filter 30 only transmits light of a specific wavelength which corresponds to a specific wavelength from a light source (not shown). The specific wavelengths of light are realized in red, green and blue colors.
The upper alignment film 24a and the lower alignment film 24b align the liquid crystal that is injected between the upper plate UP and the lower plate DP.
The TFT shown in FIGS. 1A and 1B includes a gate electrode 6 connected to the gate line (not shown) for switching the drive of the liquid crystal cell, a source electrode 8 connected to the data line (not shown), and a drain electrode 10 connected to the pixel electrode 22 through a contact hole 20. The TFT further includes a gate insulating film 12 for insulating the gate electrode 6, the source electrode 8 and the drain electrode 10; a semiconductor layer made of layers 14, 16 for forming a channel between the source electrode 8 and the drain electrode 10 using a gate voltage supplied to the gate electrode 6. The TFT selectively supplies the data signal from the data line to the pixel electrode 22 in response to the gate signal from the gate line.
The pixel electrode 22 is located at the cell area divided by the data line and the gate line and is formed of a transparent conductive material that has a high light transmittance. The pixel electrode 22 is formed on a passivation film 18 that is spread on the entire surface of the lower substrate 1 and is electrically connected to the drain electrode 10 through the contact hole 20. The contact hole 20 is formed to penetrate the passivation film 18.
The ball spacer 36 is formed between the upper plate UP and the lower plate DP and acts to provide a space into which the liquid crystal material can be injected. The ball spacer 36 is formed by spraying on at least any one of the substrates 1, 31 of the upper plate UP and the lower plate DP.
Further, the ball spacer 36 of the related art may be a plurality of ball spacers. The plurality of ball spacers may be uniformly scattered for uniformly keeping a cell gap of the liquid crystal cell. However, it is difficult to uniformly scatter the plurality of ball spacers because of a limitation in the uniformity of the scattering method. When the plurality of ball spacers is scattered non-uniformly, the cell gap becomes non-uniform. This causes the problematic generation of a spot in a screen.
Further, if a pressure is applied to a display area of the LCD panel, the ball spacer 36 moves between the upper plate UP and the lower plate DP. This causes the generation of a ripple phenomenon, where an image displayed in the display area becomes dark in a wave shape.
A column spacer that is fixed at a specific location to be patterned, and a patterning method thereof, has been developed for solving the above problem. However, the column spacer is formed by a photolithography process so that not less than 95% of a spacer material is removed. Thus, the usage rate of the material is not good and its fabrication process is complicated.
In order to reduce the waste of the material and the number of processes in the fabrication process, there has been developed a method for forming a ball spacer by using an ink-jet spraying device. The ball spacer forming method using the ink-jet spraying device is a method which can control the location where the ball spacer is to be formed. Thus, the ink-jet spraying device is different from the ball spacer scattering method of the related art which has the limitation in the uniformity thereof.
FIG. 2 is a diagram representing that a ball spacer 36 is disposed at a fixed point of a non-display area 2 by an ink-jet method. However, even though the ball spacer 36 is disposed at the fixed point of the desired location by the ink-jet method, the ball spacer 36 can be made to move by pressure, oscillation, impact, etc. which are applied in a process after the formation of the ball spacer 36. Accordingly, in the related art LCD panel, the ball spacer 36 moves to the display area of the color filter 30. FIG. 3 is a diagram representing a phenomenon that a ball spacer 36 shown in FIG. 2 moves after being disposed. This causes deterioration in a cell gap uniformity of the LCD panel and deterioration in a contrast ratio.